1. Technical Field
The present invention relates to an optical scanning element and an image display apparatus, and more particularly to a technology of an optical scanning element included in an image display apparatus.
2. Related Art
Currently, a technology of an image display apparatus which uses laser beam source as a light source has been proposed. The laser beam source has been developed as light source for image display apparatus such as projector and display with the demand for higher output and multi-coloration of the image display apparatus. The laser beam source has several advantages such as high color reproducibility, capability of immediate turn-on, and long life compared with a UHP lamp used as a light source of a projector or the like in related-art. Moreover, when compared with a related-art light source, the laser beam source achieves higher light emission efficiency and only requires a smaller number of optical elements with reduction of energy loss. Thus, the laser beam source contributes to power-saving of the device. An example of the image display apparatus which performs laser beam scanning uses laser beam modulated according to an image signal. The image display apparatus using laser beam for scanning generally includes a light source system, a combining system for combining a plurality of color lights into one light, and a scanning system for scanning by the combined light. Since these systems may be formed by separate devices or elements, size reduction and cost reduction of the laser beam scanning type image display apparatus are expected.
A typical optical scanning device is constituted by polygon mirror or galvanomirror in related art. For display of a high-resolution image, high-speed laser beam scanning is required. On the other hand, for display of a large screen from a short distance, the scanning angle needs to be large. For meeting these requirements, MEMS (micro electro mechanical system) mirror has been currently drawing attention. The MEMS mirror capable of reducing the size of a driving unit for achieving extremely small and high-speed driving contributes to miniaturization. The typical MEMS mirror is sealed within a package for driving. For achieving high-speed and wide-range scanning, pressure within the sealed package is decreased to reduce the air resistance of the MEMS mirror due to the trade-off relationship between the scanning speed and scanning angle. It is also preferable that dust-prevention sealing package is provided since adhesion of foreign material such as dust causes breakage of the structure. The package for sealing the MEMS mirror is made of transparent material capable of transmitting light entering the MEMS mirror and light reflected by the MEMS mirror (for example, see JP-A-9-159937).
A part of light advancing to the MEMS mirror is reflected by the surface of the transparent material provided on the package. The intensity of the light reflected by the MEMS mirror is distributed by scanning, but the intensity of the light reflected by the surface of the transparent material is not distributed. In this case, the light reflected by the surface of the transparent material becomes conspicuous after entrance into a scanning area even when the intensity is low. As a result, the image quality lowers by the presence of constant spot at a position within the image regardless of the contents of the image.